Speed control system for alternating current induction motors

ABSTRACT

A speed control system for alternating current induction motors wherein a reference potential, which is a rectified phase of the alternating current supply potential, is connected across the series combination of a charge circuit resistor and the timing capacitor of a unijunction transistor type relaxation oscillator circuit and a direct current control potential, which is a function of motor speed, is connected across the charge circuit resistor through a speed control resistor in series. The unijunction transistor type relaxation oscillator circuit and associated circuitry produces a trigger signal at the electrical angle of each potential cycle of each phase of the alternating current supply potential as determined by the difference of magnitude between the reference potential and the control potential impressed across the charge circuit resistor which trigger respective silicon controlled rectifiers conductive to complete an energizing circuit for the corresponding phase winding of the motor. An external source of electrical signals which vary in magnitude in response to changes of conditions which require a change of motor speed is connected across the speed control resistor for varying the speed of the controlled motor.

United States Patent [191 Primary Examiner-Gene Z Rubinson A ttorney-Eugene W. Christen, Creighton R. Meland and Richard G. Stahr Pryjmak [451 May 22, 1973 [5 SPEED CONTROL SYSTEM FOR [57] ABSTRACT Q b gg CURRENT INDUCTION A speed control system for alternating current induction motors wherein a reference potential, which is a [75] Inventor: Bohdan I. Pryjmak, Dayton, Ohio rectified phase of the alternating current supply poten- [73] Assigneez General Motors Corporation, tial, is connectedacross the serl es combinat ion of a charge circuit resistor and the timing capacitor of a Detroit, Mich.

UI'lljUllCtlOIl transistor type relaxatlon oscillator circuit [22] Filed: Aug. 11, 1971 and a direct current control potential, which is a func- [21] AppL No: 170,765 tion of motor speed, is connected across the charge circuit resistor through a speed control resistor in series. The unijunction transistor type relaxation oscillator circuit and associated circuitry produces a trigger 318/345 signal at the electrical angle of each potential cycle of [5 lift. Cl. ..H02p each phase of the alternating current upply potential I Fleld of Search l as determined the difference of magnitude between 318/345 the reference potential and the control potential impressed across the charge circuit resistor which trigger [56] Reie'ences C'ted respective silicon controlled rectifiers conductive to UNITED STATES PATENTS complete energizing circuit for the corresponding phase winding of the motor. An external source of 3,387,196 6/1968 Graham et a]. ..3l8/345 X electrical signals which vary in magnitude in response 3,506,899 4/1970 Graham ..3l8/227 to changes of conditions which require a change of motor speed is connected across the speed control resistor for varying the speed of the controlled motor.

4 Claims, 4 Drawing Figures TO ONE PHA SE OF SUPPLY POTENTIAL j] "Mohe an? MULTIVIBRATOR fig MULTIVIBRATOR l Patented May 22, 1973 I 3,735,222

2 Sheets-Sheet l TO ONE PHASE'OF SUPPLY POTENTIAL TO ONE PHA.SE OF SUPPLY POTENTIAL fim/ MONOSTABLE MULTIVIBRATOR iiu) L ii iim

MONOSTABL'E MULTIVIBRATOR i7u i);

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ATTORNEY Patentd May 22, 1973 2 Sheets-Sheet 2 lim Mm KMIM ATTQRNFV SPEED CONTROL SYSTEM FOR ALTERNATING CURRENT INDUCTION MOTORS The present invention relates to motor speed control systems and, more specifically, to a speed control system for alternating current induction motors wherein the speed of a controlled motor is varied in response to an externally generated electrical signal which varies in magnitude with changes of conditions which require a change of motor speedv Alternating current induction motors have discrete phase windings corresponding to each phase of a compatible alternating current supply potential which are energized by the phase of the alternating current supply potential to which they correspond. The number of coils per phase winding may vary depending upon the number of poles designed into the motor. Motors of this type normally operate at a constant, fixed speed which is determined by the frequency of the alternating current supply potential and the number of magnetic poles produced by the phase windings.

In certain applications where motors of this type may be advantageously used, it may be desirable to operate the motor at variable speeds. To change the speed of alternating current induction motors, it has heretofore been necessary to change the frequency of the alternating current supply potential or the number of magnetic poles produced by the phase windings. Both of these alternatives have been unsatisfactory in that the former requires expensive frequency converting equipment and the latter provides, at best, step-by-step control through compound switching arrangements.

It has been found that the speed of alternating current induction motors may be smoothly adjusted over a wide range by controlling the electrical conduction angle during which each potential cycle of each phase of the alternating current supply potential energizes the corresponding phase windings. To reduce the speed, the respective phase windings are energized over a shorter electrical conduction angle of each potential half-cycle of the corresponding phase. For optimum operation at any speed, the conduction angle of the potential cycles of all phases should be equal to the conduction angle of the potential cycles of one of the phases selected to be the reference phase.

In another United States patent application, Ser. No. 493,652, filed Oct. 7, 1965, now U.S. Pat. No. 3,387,l96, and assigned to the same assignee as that of the present application, a novel speed control system which may be used with any alternating current induction motor of the type having discrete phase windings corresponding to each phase of a compatible alternating current supply potential for manually changing motor speed is disclosed in detail. Briefly, the speed control system so disclosed is responsive to a difference of magnitude between a direct current reference potential and a direct current control potential, which is not only a function of motor speed but is also independently, manually variable to vary the speed of the motor, to produce an electrical trigger signal at the electrical angle of each potential half-cycle of each phase of the alternating current supply potential as determined by the selected motor speed for operating respective trigger signal responsive switching devices which establish respective phase winding energizing circuits when operated to close by the trigger signals. In this system, the greater the difference of magnitude between the reference and control potentials, the earlier during each potential half-cycle of each phase of the alternating current supply potential the corresponding motor phase winding is energized to increase the speed of the motor.

There are many applicationswhich require the speed of the motor to be automatically changed in response to changes of external conditions which require a change of motor speed and which require the operating range of the motor to be changed to satisfy the requirements of a variety of applications with the same control circuit.

It is, therefore, an object of this invention to provide an improved motor speed control system for alternating current induction motors of the type which produces electrical trigger signals at the electrical angle of each potential cycle of each phase of the alternating current supply potential as determined by the difference of magnitude between a direct current reference potential and a direct current control potential which are applied across the gate-cathode electrodes of respective silicon controlled rectifiers for triggering these devices conductive to complete an energizing circuit for the corresponding phase winding which is responsive to an externally generated electrical signal which varies in magnitude with changes of conditions which require a change of motor speed.

It is another object of this invention to provide an improved speed control system for alternating current induction motors of the type which produces an electrical trigger signal at the electrical angle of each potential cycle of each phase of the alternating current supply potential as determined by the difference of magnitude between a direct current reference potential and a direct current control potential for triggering respective silicon controlled rectifiers conductive to complete an energizing circuit for the respective phase windings of the motor which is responsive to an externally generated electrical signal which varies in magnitude with changes of conditions which require a change of motor speed and is readily adaptable to a change of motor operating range to satisfy the requirements of a variety of applications.

In accordance with this invention, a motor speed control system for alternating current induction motors of the type which produces an electrical trigger signal at the electrical angle of each potential cycle of each phase of the alternating current supply'potential as determined by the of magnitude between a direct current reference and a direct current control potential for triggering respective silicon controlled rectifiers conductive to complete an energizing circuit for the corresponding phase winding of the motor is provided wherein the difference of magnitude between the reference and control potentials is established by an externally generated electrical signal which varies in magnitude with changes of conditions which require a change of motor speed.

For a better understanding of the present invention, together with additional objects, advantages and features thereof, reference is made to the following description and accompanying drawings in which:

FIG. 1 is a schematic diagram of the improved motor speed control system for alternating current induction motors of this invention;

FIG. 1A is a schematic diagram of an alternate embodiment which may be interconnected in the circuit of FIG. 1;

FIG. 2 is a schematic diagram of the switching system for a wye connected alternating current induction motor which may be used with the circuitry schematically set forth in FIG. 1; and

FIG. 3 is a schematic diagram of the switching system for a delta connected alternating current induction motor which may be used with the circuitry schematically set forth in FIG. 1.

The novel speed control system of this invention may be employed with any alternating current induction motor of the type having discrete phase windings corresponding to each phase of a compatible alternating current supply potential.

For purposes of illustrating the novel features of this invention and without intention or inference of a limitation thereto, the following detailed description will be in regard to both wye and delta connected three-phase alternating current induction motors.

To establish an energizing circuit for each motor phase winding across the corresponding phase of the alternating current supply potential, respective controllable switching circuit devices, which may be silicon controlled rectifiers, responsive to electrical trigger signals are provided.

In FIG. 2, silicon controlled rectifier 10 corresponds to phase A and, when conducting, completes an energizing circuit for the phase windings corresponding to phase A through the phase windings corresponding to phase B. Silicon controlled rectifier 11 corresponds to phase B and, when conducting, completes an energizing circuit for the phase windings corresponding to phase B through the phase windings corresponding to phase C. Silicon controlled rectifier 12 corresponds to phase C and, when conducting, completes an energizing circuit for the phase windings corresponding to phase C through the phase windings corresponding to phase A. With both silicon controlled rectifiers l and 11 conducting, phase A may feed both phases B and C; with both silicon controlled rectifiers l1 and 12 conducting, phase B may feed both phases C and A and with both silicon controlled rectifiers l2 and conducting, phase C may feed both phases A and B.

In FIG. 3, the parallel combination of oppositely poled silicon controlled rectifiers 13 and 14 correspond to phase A and are connected in series with the phase winding corresponding to phase A, the parallel combination of oppositely poled silicon controlled rectifiers 15 and 16 correspond to phase B and are connected in series with the phase winding corresponding to phase B and the parallel combination of oppositely poled silicon controlled rectifiers l7 and 18 correspond to phase C and are connected in series with the phase winding corresponding to phase C.

With single and two-phase applications, one and two switching devices, respectively, are required. With applications of more than three phases, one or two switching devices corresponding to each phase may be required depending upon the configuration in which the phase windings are connected.

As the point of reference or ground potential is the same point electrically throughout the system, it has been illustrated by the accepted schematic symbol and referenced by the numeral 5 in FIG. 1 of the drawings.

That portion of the circuit of FIG. 1 including a unijunction transistor type relaxation oscillator circuit comprising unijunction transistor 20, timing capacitor 25 and base resistors 22 and 23; type NPN transistor 30 and transformer 26 having a primary winding 27 and two secondary windings 28 and 29 and the blocks referenced by the numerals 34 and 35 comprise circuitry responsive to a difference of magnitude between a direct current reference potential and a direct current control potential for producing a trigger signal at the electrical angle of each potential cycle of each phase of the alternating current supply potential as determined by the magnitude of the difference.

The circuitry represented by blocks 34 and 35 may be conventional monostable multivibrator circuits well known in the art. Consequently, as these circuits per se form no part of this invention, each has been illustrated in block form.

The circuitry comprising the unijunction transistor type relaxation oscillator circuit, type PNP transistor 30 and transformer 26 is a master trigger signal producing circuit which produces a trigger signal at the electrical angle of each potential cycle of the reference phase of the supply potential as determined by the magnitude of the difference between the reference and control potentials.

Each of monostable multivibrator circuits 34 and 35 is a slave trigger signal producing circuit connected in cascade with the master trigger signal producing circuit and responsive to the trigger signal produced by the next preceding trigger signal producing circuit to produce a trigger signal corresponding to a respective other phase of the alternating current supply potential and spaced from each other by an electrical angle equal to the electrical angle between phases of the alternating current supply potential.

To produce a direct current reference potential in synchronism with a selected phase of the supply potential, one phase of the alternating current supply potential may be rectified by a full-wave diode bridge rectifier circuit, generally shown by reference numeral 8 in FIG. 1 and hereinafter referred to as the source of reference potential, which produces a pulsating direct current potential, hereinafter referred to as the reference potential.

The reference potential, which may be regulated by a Zener diode 24, is connnected across the series combination of a first impedance element, which may be a charge circuit resistor 36, and timing capacitor 25 through a reference potential loop circuit which may be traced from the positive polarity direct current output terminal of rectifier circuit 8, through resistor 37, lead 38, the parallel combination of capacitor 44, resistor 45, and diode 47, variable resistor 48 and resistor 49 in series, through charge circuit resistor 36, lead 50, timing capacitor 25 and point of reference or ground potential 5 to the negative polarity direct current output terminal of rectifier circuit 8.

Timing capacitor 25 is charged by the reference potential and, when the charge thereupon, which is applied across the emitter electrode 21 and one of the base electrodes of unijunction transistor 20, reaches a magnitude substantially equal to the peak point potential of unijunction transistor-20, this device switches to a'low resistance or conducting state. With unijunction transistor 20 conducting, timing capacitor 25 discharges through the emitter-ba se junction of unijunction transistor 20 and base resistor 23. When the potential applied to emitter electrode 21 decreases to a value which is of insufficient magnitude to maintain unijunction transistor 20 conducting as timing capacitor 25 discharges, the unijunction transistor 20 reverts to its high resistance or nonconducting state and the cycle just described is repeated. Upon each discharge of timing capacitor 25 through base resistor 23, a trigger signal potential is produced thereacross which is of a positive polarity upon junction 51 with respect to point of reference or ground potential 5.

As only one trigger signal is required during each potential cycle of each phase and since the relaxation os cillator circuit is normally free-running, as described in the preceding paragraph, it is necessary that the relaxation oscillator circuit be disenabled during the remainder of each potential cycle after a trigger signal has been produced. To disenable the relaxation oscillator circuit upon the production of a trigger signal, silicon controlled rectifier 40 is provided. The trigger signal appearing across resistor 23 is applied through coupling capacitor 52 across the gate-cathode electrodes of silicon controlled rectifier 40 in the proper polarity relationship to produce conduction through the anodecathode electrodes thereof. Conducting silicon controlled rectifier 40 removes the inter-base potential from unijunction transistor 20 as conducting silicon controlled rectifier 40 is substantially a short circuit across the direct current terminals of rectifier bridge 8.

The trigger signal appearing across base resistor 23 is also applied through coupling capacitor 52 across the base electrode 31 and emitter electrode 33 of type NPN transistor 30 in the proper polarity relationship to produce base-emitter current flow through this type NPN transistor. The resulting current flow through collector electrode 32 and emitter electrode 33 completes an energizing circuit for primary winding 27 of transformer 26. As the flow of current through primary winding 27 increases from zero, a potential is induced in each of secondary windings 28 and 29. The potential induced in secondary winding 28, which is poled in such a manner that the potential upon output terminal 53(1) is of a positive polarity with respect to output terminal 54(1), is applied across the gate-cathode electrodes of silicon controlled rectifier of FIG. 2 through output terminals 53(1) and 54(1) of FIG. 1 and input terminals 53(2) and 54(2) of FIG. 2, respectively, in the proper polarity relationship to trigger silicon controlled rectifier 10 conductive to complete an energizing circuit for phase winding A through phase winding B. The potential induced in secondary winding 29 triggers monostable multivibrator 34 to the alternate state to complete an energizing circuit for primary winding 67 of transformer 66. Monostable multivibrator 34 remains in the alternate state for a period of time corresponding to 120 electrical degrees, the number of electrical degrees between phases of a three-phase supply potential, and spontaneously returns to the'stable state to interrupt the energizing circuit for primary winding 67. The resulting collapsing magnetic field induces a potential in each of secondary windings 68 and 69. The potential induced in secondary winding 68, which is poled in such a manner that the potential upon output terminal 55(1) is of a positive polarity with respect to output terminal 56(1), is applied across the gate-cathode electrodes of silicon controlled rectifier ll of FIG. 2 through output terminals 55(1) and 56(1) of FIG. 1 and input terminals 55(2) and 56(2) of FIG. 2, respectively, in the proper polarity relationship to trigger silicon controlled rectifier l1 conductive to complete an energizing circuit for phase winding B through phase winding C. The potential induced in secondary winding 69 triggers monostable multivibrator 35 to the alternate state to complete an energizing circuit for primary winding 77 of transformer 76. Monostable multivibrator 35 remains in the alternate state for a period of time corresponding to 120 electrical degrees and spontaneously returns to the stable state to interrupt the energizing circuit for primary winding 77. The resulting collapsing magnetic field induces a potential in secondary winding 78 of a positive polarity upon output terminal 57(1) with respect to output terminal 58(1) which is applied across the gate-cathode electrodes of silicon controlled rectifier 12 of FIG. 2 through output terminals 57(1) and 58(1) of FIG. 1 and input terminals 57(2) and 58(2) of FIG. 2, respectively, to trigger this device conductive to complete an energizing circuit for phase winding C through phase winding A. The circuitry of FIG. 1 may also be used with a delta connected induction motor as shown in FIG. 3. To connect the configuration of FIG. 3 into the circuitry of FIG. 1, coils 59 and 60 of FIG. 3 are magnetically coupled to primary winding 27 of FIG. 1 in place of secondary winding 28, coils 61 and 62 of FIG. 3 are magnetically coupled to primary winding 67 of FIG. 1 in place of secondary winding 68 and coils 63 and 64 of FIG. 3 are magnetically coupled to primary winding 77 of FIG. 1 in place of secondary winding 78. The coils of FIG. 3 are, of course, so poled to produce the correct potential polarity relationship across the gate-cathode electrodes of each respective silicon controlled rectifler. A complete detailed description of this circuit is set forth in the afore-referenced U.S. Pat. No. 3,387,196.

The conduction angle over which each phase winding of a controlled motor is energized by the corresponding phase of the supply potential is determined by the electrical angle during each potential cycle of each phase of the supply potential at which each respective trigger signal is produced, the earlier during each potential half cycle that the trigger signal is produced, the greater the conduction angle. The speed of the controlled motor, of course, increases with an increase of the conduction angle.

Timing capacitor 25 begins to charge with the appearance of the reference potential and triggers unijunction transistor 20 to conduction to produce a master trigger signal across base resistor 23 at the electrical angle of each cycle of the reference phase of the supply potential at which the charge upon timing capacitor 25 has reached a magnitude substantially equal to the peak point potential of unijunction transistor 20. To change the conduction angle, therefore, the time required for the charge on timing capacitor 25 to reach a magnitude substantially equal to the peak point potential of unijunction transistor 20 may be varied.

In capacitor charging circuits, the capacitor will charge substantially exponentially to substantially full potential in a period of time which is substantially equal to four times the time constant of the circuit regardless of the magnitude of the potential to which it is charged. Therefore, the initial substantially linear rate of charge is determined, to a great extent, by the magnitude of the potential charge, the greater the magnitude of the charge the greater the initial rate.

According to Kirchoffs second law, the sum of the potential drops in any complete or closed circuit must equal the sum of the potential rises in that circuit. In

applying this law, tracing through any single circuit, whether it is by itself or a part of a network, a potential drop exists when tracing through a resistance with or in the same direction as the current or through a battery or generator against their potential, from positive to negative, and a voltage rise exists when tracing through a resistance against or in a direction opposite to the current, or through a battery or a generator in a direction with their potential, negative to positive.

Considering Zener diode 24 of the reference potential loop as a potential generator, the sum of the potential drops across the parallel combination of capacitor 44, resistor 45, and diode 47, variable resistor 48 and resistor 49 in series across charge circuit resistor 36, across timing capacitor 25 and the interconnecting wires must equal the potential rise across Zener diode 24. Consequently, the magnitude of the potential charge upon timing capacitor 25 is equal to the potential drop thereacross in this loop.

As the circuit components included in the reference potential loop just considered and the frequency and amplitude of the alternating current supply potential and, therefore, the reference potential, remain substantially constant, the variable parameter necessary to control motor speed my be a direct current control potential, which is related to and varies in magnitude with motor speed and which may be varied in magnitude in response to an external influence for varying the speed of the motor, applied across charge circuit resistor 36 through a second impedance element in series, which may be a speed control resistor 46.

One method for producing a direct current control potential which varies with motor speed is an electric tachometer driven by the motor shaft which produces a direct current output potential of a magnitude proportional to motor speed. Commercially available tachometers of this type are small direct current generators which produce a direct current output potential which increases and decreases linearly in magnitude with increases and decreases of motor speed. As electrical tachometers of this type are well known in the art and form no part of this invention, it has been schematically illustrated as a circle in FIG. 1 and referenced by the numeral 9. The output direct current potential of tachometer 9 will hereinafter be referred to as the control potential.

The control potential is connected across charge circuit resistor 36 through speed control resistor 46 in series through a control potential loop circuit which may be traced from the positive polarity output terminal of tachometer 9, through potentiometer 71, diode 72, speed control resistor 46, variable resistor 73, diode 74, charge circuit resistor 36 and lead 50 to the negative polarity terminal of tachometer 9. With the control potential applied across charge circuit resistor 36, this device may be considered a potential generator. Tracing through the control potential loop in the same direction and with the control potential applied across charge circuit resistor 36 poled as shown in FIG. I, the potential appearing across charge circuit resistor 36 is a potential drop for purposes of Kirchoffs second law. As

the reference potential across Zener diode 24 and the value of the circuit components remain substantially constant, the increase in magnitude of the potential drop across charge circuit resistor 36 introduced by the control potential applied thereacross must be accompanied by a corresponding decrease in potential drop across timing capacitor 25 to satisfy Kirchoffs second law. As the potential drop across timing capacitor 25 determines the magnitude of the charge thereon, the initial rate of charge of timing capacitor 25 and, therefore, the time required for the charge to increase in magnitude to the peak point potential of unijunction transistor 20 is determined by the magnitude of the difference between the reference and control potentials, which may be varied by varying the magnitude of the control potential applied across charge circuit resistor 36. Consequently, the speed of a controlled motor may be varied by varying the magnitude of the control potential in response to an external influence.

The magnitude of the control potential across charge circuit resistor 36 may be varied by an external source of electrical signals, which vary in magnitude in response to changes of conditions which require a change of motor speed, applied across speed control resistor 46 for varying the speed of a controlled motor.

One example of an external source of electrical signals which vary in magnitude in response to changes of conditions which require a change of motor speed is set forth in FIG. 1 and includes a source of selectively variable regulated direct current potential 41, one example of which is set forth in schematic form, a potentiometer 91 having a movable contact 92 and a pressure transducer 93 having two input terminals 94 and 95 and a movable contact 96 operated by changes of pressure. Terminal ends 91a and 91b of potentiometer 91 and the input terminals 94 and 95 of pressure transducer 93 are connected across the source of selectively variable regulated direct current potential 41 through respective leads 98 and 99. The pressure transducer 93 is schematically set forth in FIG. 1 which illustrates movable contact 96 to be operated by a pressure sensitive diaphragm 97. Pressure transducers of this type are commercially available from H. E. Sostman Co., Cranford, New Jersey.

To apply the external source of electrical signals across the speed control resistor 46, movable contact 92 of potentiometer 91 and movable contact 96 of pressure transducer 93 are connected across speed control resistor 46 through lead 101 and through lead 102 and diode 103, respectively. Without intention or inference of a limitation thereto, in FIG. 1, movable contact 96 of pressure transducer 93 is illustrated as being connected to the same end of speed control resistor 46 as the source of control potential 9 with movable contact 92 of potentiometer 91 being connected to the other end of speed control resistor 46.

Considering potentiometer 71 of the control potential loop as a potential generator, in accordance with Kirchoffs second law, the sum of the voltage drops across diode 72, speed control resistor 46, variable resistor 73, diode 74, charge circuit resistor 36 and the interconnecting leads must equal the potential rise across that portion of potentiometer 71 between the negative polarity output terminal of tachometer 9 and movable contact 71a thereof. For any setting of potentiometer 71 and variable resistor 73, the magnitude of the control potential drop across charge circuit resistor 36 may be varied by an externally generated electrical signal impressed across speed control resistor 46 which, for purposes of Kirchoffs second law, may be considered a potential generator in the control potential loop.

Tracing through the control potential loop in the same direction with a source of externally generated electrical signals applied across speed control resistor 46 and poled as shown in FIG. 1, the potential drop across speed control resistor 46 produced by externally generated electrical signal current flow therethrough is a potential drop for purposes of Kirchoffs second law. Consequently, an increase or a decrease of magnitude of potential drop across speed control resistor 46 as a result of an increase or decrease of magnitude of the externally generated electrical signal must be accompanied by a corresponding respective decrease or increase of control potential drop across charge circuit resistor 36 to satisfy Kirchoffs second law. As was brought out in the application of Kirchoffs second law to the reference potential loop, a decrease or increase of control potential drop across charge circuit resistor 36 must be accompanied by a corresponding respective increase or decrease of potential drop across timing capacitor 25 of the reference potential loop to satisfy Kirchoffs second law. With the source of externally generated electrical signals poled the other way across speed control resistor 46, the potential drop across speed control resistor 46 produced by externally generated electrical signal current flow therethrough is a potential rise for purposes of Kirchoffs second law. Consequently, an increase or decrease of magnitude of potential drop across speed control resistor 46 as a result of an increase or decrease of magnitude of the externally generated electrical signal will produce a corresponding respective decrease or increase of control potential drop across capacitor 25. As an increase of control potential drop across timing capacitor 25 in the reference potential loop increases the speed of a controlled motor and a decrease of control potential drop across timing capacitor 25 decreases the speed of a controlled motor, it is apparent that the speed of a controlled motor may be varied through the influence of an external source of electrical signals applied across speed control resistor 46 which vary in response to conditions which require a change of motor speed.

Referring to FIG. 1 of the drawing, the magnitude of the externally generated electrical signal applied across speed control resistor 46 is equal to the potential drop across movable contact 96 of pressure transducer 93 and movable contact 92 of potentiometer 91. Should the externally generated electrical signal be of a positive polarity upon movable contact 92 of potentiometer 91 with respect to movable contact 96 of pressure transducer 93, the externally generated electrical signal is ineffective as diode 103 blocks externally generated electrical signal current flow through speed control resistor 46. Consequently, the potential drop across speed control resistor 46 as a result of the externally generated electrical signal with the arrangement of FIG. I is always of a positive polarity upon terminal end 46a of resistor 46 with respect to terminal end 46b.

creases the speed of a controlled motor with increases of pressure. A decrease of pressure, of course, results in a movement of movable contact 96 of potentiometer 93 in a direction toward input terminal 95 to decrease the magnitude of the externally generated electrical signal impressed across speed control resistor 46. The resulting decrease of externally generated electrical signal potential drop across speed control resistor 46 is accompanied by a corresponding decrease of potential drop across timing capacitor 25, a condition which reduces the speed of a controlled motor.

The maximum speed of a controlled motor may be adjusted by adjusting the magnitude of the output direct current potential of source 41, the low operating speed of the motor may be determined by adjusting variable resistor 73 and the pressure at which the speed of the motor begins to increase may be selected by adjusting movable contact 92 of potentiometer 91.

With the specific application with which the circuit of this invention has been hereinabove described in detail, an increase and decrease of magnitude of the externally generated electrical signal resulted in a respective increase and decrease of the speed of a controlled motor. With applications which require that the speed of a controlled motor increase and decrease with respective decreases and increases of magnitude of the externally generated electrical signal, the externally generated electrical signal must be impressed across speed control resistor 46 in a polarity relationship opposite that shown in FIG. 1.

Another example of an external source of electrical signals suitable for use with the circuit of this invention is set forth in FIG. 1A wherein a current signal source is shown connected across speed control resistor 46. As current signal source 105 may be any one of the several well known in the art, such as that commercially available from Fischer & Porter Company, Warminster, Pennsylvania, it has been set forth in block form in FIG. 1A. The potential drop produced across speed control resistor 46 in response to changes of magnitude of the signals produced by current signal source 105 affects the speed control circuit of this invention in the same manner as previously described to vary the speed of a controlled motor.

Upon motor start in the absence of an externally generated electrical signal, the control potential is zero, consequently, the magnitude of the difference between the reference and control potentials is maximum. Consequently, the full charging potential of the reference potential is applied across timing capacitor 25 to rapidly charge this device to the peak point potential of unijunction transistor 20. As this point occurs substantially at the beginning of each potential cycle of the reference phase, substantially full potential is applied across the motor.

To establish the difference of magnitude between the reference potential and the control potential at substantially zero upon motor start in the absence of an externally generated electrical signal and to increase the difference in magnitude at a predetermined rate to a maximum, a capacitor 75 may be connected across the series combination of control resistor 36 and timing capacitor 25 through a circuit which may be traced from junction 39, through diode 81, resistor 82, capacitor 75 to point of reference or ground potential 5.

Upon motor start, normally closed contact 65, which may be one of the normally closed contacts of the assocharge through diode 81 and resistor 82. With capacitor 75 charging, junction 39 is at substantially ground potential. Consequently charging capacitor 75 establishes the difference in magnitude between the reference and control potentials, and consequently the magnitude of the charging potential for timing capacitor 25, at substantially zero upon motor start. Capacitor 85, however, begins to charge through variable resistor 86 and resistor 87 until it has reached a magnitude equal to the peak point potential of unijunction transistor 70. Upon the conduction of unijunction transistor 70, capacitor 85 discharges through the emitter-base junction thereof and base resistor 23 to produce a trigger potential signal thereacross of a positive polarity upon junction 51 with respect to point of reference or ground potential 5. This trigger signal gates silicon controlled rectifier 40 conductive to disenable the master trigger signal producing circuit for the remainder of this potential cycle, provides a trigger signal across output terminals 53(1) and 54(1) and initiates the action of the slave trigger signal circuitry in a manner previously described. By properly adjusting variable resistor 86, the electrical angle at which capacitor 85 has become charged to the peak point potential of unijunction transistor 70 may be established near the end of each positive polarity half-cycle of the reference phase of the supply potential. Consequently, the trigger signal for each potential cycle of the supply potential occurs near the end of each positive polarity half-cycle to provide a reduced voltage across the motor upon start.

As capacitor 75 continues to charge and the controlled motor begins to run, the potential upon junction 39 begins to increase in magnitude and the magnitude of the control potential across charge circuit resistor 36 increases. Consequently, the magnitude of the difference between the reference and control potentials and, consequently, the charging potential for timing capacitor 25 begins to increase in magnitude. This increase in magnitude charges timing capacitor earlier during each potential cycle of the reference phase of the supply potential to produce the trigger signals earlier during each potential half-cycle of each phase of the supply potential to increase the conduction angle and, consequently, the speed of the controlled motor. The difference in magnitude between the reference and control potentials and, consequently, the charging potential for timing capacitor 25 continues to increase at a predetermined rate as determined by the time constant of the charging circuit for capacitor 75 to a maximum. Consequently, the speed of the motor continues to increase until it is operating at a speed as determined by the magnitude of the control potential across charge circuit resistor 36 and capacitor 75 is of no further consequence although it continues to take a charge through diode 90 until charged to the full reference potential. As the capacitor 75 is no longer effective, the speed control system operates in the normal manner.

Upon the shutdown of the controlled motor, the normally closed contacts 65 of the associated controller relay close to discharge capacitor 75 and prepare the system for the next motor start.

While a preferred embodiment of the present invention has been shown and described, it will be obvious to those skilled in the art that various modifications and substitutions may be made without departing from the spirit of the invention which is to be limited only within the scope of the appended claims.

What is claimed is:

l. A speed control system for alternating current motors of the type having discrete phase windings corresponding to each phase of a compatible alternating current supply potential comprising, means for producing a reference potential in synchronism with a selected phase of said alternating current supply potential, means for producing a control potential which varies in magnitude with changes of motor speed, means including a unijunction transistor type relaxation oscillator circuit having a timing capacitor responsive to a difference in magnitude between said reference potential and said control potential for producing a trigger signal at the electrical angle of each potential cycle of each phase of said alternating current supply potential as determined by the magnitude of said difference, first and second impedance elements, means for connecting said reference potential across the series combination of said first impedance element and said timing capacitor, means for connecting said control potential across said first impedance element through said second impedance element in series in the same polarity relationship as said reference potential, an external source of electrical signals which vary in magnitude in response to changes of conditions which require a change of motor speed, means for applying said external source of electrical signals across said second impedance element for varying the speed of said motor, and controllable switching circuit means corresponding to each phase of said alternating current supply potential for completing an energizing circuit for the corresponding said phase windings in response to respective said trigger signals.

2. A speed control system for alternating current motors of the type having discrete phase windings corresponding to each phase of a compatible alternating current supply potential comprising, means for producing a reference potential in synchronism with a selected phase of said alternating current supply potential, means for producing a control potential which varies in magnitude with changes of motor speed, means including a unijunction transistor type relaxation oscillator circuit having a timing capacitor responsive to a difference in magnitude between said reference potential and said control potential for producing a trigger signal at the electrical angle of each potential cycle of each phase of said alternating current supply potential as determined by the magnitude of said difference, first and second impedance elements, means for connecting said reference potential across the series combination of said first impedance element and said timing capacitor, means for connecting said control potential across said first impedance element through said second impedance element in series in the same polarity relationship as said reference potential, a source of selectively vari-, able regulated direct current potential, a potentiometer having a movable contact, a pressure transducer of the variable resistance type having two input terminals and a movable contact operated by changes of pressure, means for connecting said potentiometer across said source of selectively variable regulated direct current potential, means for connecting said input terminals of said pressure transducer across said source of selectively variable regulated direct current potential, means for connecting said movable contact of said potentiometer and said movable contact of said pressure transducer across said second impedance element, and controllable switching circuit means corresponding to each phase of said alternating current supply potential for completing an energizing circuit for the corresponding said phase windings in response to respective said trigger signals.

3. A speed control system for alternating current motors of the type having discrete phase windings corresponding to each phase of a compatible alternating current supply potential comprising, means for producing a reference potential in synchronism with a selected phase of said alternating current supply potential, means for producing a control potential which varies in magnitude with changes of motor speed, means including a unijunction transistor type relaxation oscillator circuit having a timing capacitor responsive to a difference in magnitude between said reference potential and said control potential for producing a trigger signal at the electrical angle of each potential cycle of each phase of said alternating current supply potential as determined by the magnitude of said difference, first and second impedance elements, means for connecting said reference potential across the series combination of said first impedance element and said timing capacitor, means for connecting said control potential across said first impedance element through said second impedance element in series in the same polarity relationship as said reference potential, a source of selectively variable regulated direct current potential, a potentiometer having a movable contact, a pressure transducer of the variable resistance type having two input terminals and a movable contact operated by changes of pressure, means for connecting said potentiometer across said source of selectively variable regulated direct current potential, means for connecting said input terminals of said pressure transducer across said source of selectively variable regulated direct current potential, means for connecting said movable contact of said pressure transducer to the same end of said second impedance element as said source of control potential,

means for connecting said movable contact of said potentiometer to the other end of said second impedance element, and controllable switching circuit means corresponding to each phase of said alternating current supply potential for completing an energizing circuit for the corresponding said phase windings in response to respective said trigger signals.

4. A speed control system for alternating current motors of the type having discrete phase windings corresponding to each phase of a compatible alternating current supply potential comprising, means for producing a reference potential in synchronism with a selected phase of said alternating current supply potential, means for producing a control potential which varies in magnitude with changes of motor speed, means including a unijunction transistor type relaxation oscillator circuit having a timing capacitor responsive to a difference in magnitude between said reference potential and said control potential for producing a trigger signal at the electrical angle of each potential cycle of each phase of said alternating current supply potential as determined by the magnitude of said difference, first and second impedance elements, means for connecting said reference potential across the series combination of said first impedance element and said timing capacitor, means for connecting said control potential across said first impedance element through said second impedance element in series in the same polarity relationship as said reference potential, an external source of current signals which vary in magnitude in response to changes of conditions which require a change of motor speed, means for applying said source of current signals across said second impedance element, and controllable switching circuit means corresponding to each phase of said alternating current supply potential for completing an energizing circuit for the corresponding said phase windings in response to respective said trigger signals. 

1. A speed control system for alternating current motors of the type having discrete phase windings corresponding to each phase of a compatible alternating current supply potential comprising, means for producing a reference potential in synchronism with a selected phase of said alternating current supply potential, means for producing a control potential which varies in magnitude with changes of motor speed, means including a unijunction transistor type relaxation oscillator circuit having a timing capacitor responsive to a difference in magnitude between said reference potential and said control potential for producing a trigger signal at the electrical angle of each potential cycle of each phase of said alternating current supply potential as determined by the magnitude of said difference, first and second impedance elements, means for connecting said reference potential across the series combination of said first impedance element and said timing capacitor, means for connecting said control potential across said first impedance element through said second impedance element in series in the same polarity relationship as said reference potential, an external source of electrical signals which vary in magnitude in response to changes of conditions which require a change of motor speed, means for applying said external source of electrical signals across said second impedance element for varying the speed of said motor, and controllable switching circuit means corresponding to each phase of said alternating current supply potential for completing an energizing circuit for the corresponding said phase windings in response to respective said trigger signals.
 2. A speed control system for alternating current motors of the type having discrete phase windings corresponding to each phase of a compatible alternating current supply potential comprising, means for producing a reference potential in synchronism with a selected phase of said alternating current supply potential, means for producing a control potential which varies in magnitude with changes of motor speed, means including a unijunction transistor type relaxation oscillator circuit having a timing capacitor responsive to a difference in magnitude between said reference potential and said control potential for producing a trigger signal at the electrical angle of each potential cycle of each phase of said alternating current supply potential as determined by the magnitude of said difference, first and second impedance elements, means for connecting said reference potential across the series combination of said first impedance element and said timing capacitor, means for connecting said control potential across said first impedance element through said second impedance element in series in the same polarity relationship as said reference potential, a source of selectively variable regulated direct current potential, a potentiometer having a movable contact, a pressure transducer of the variable resistance type having two input terminals and a movable contact operated by changes of pressure, means for connecting said potentiometer across said source of selectively variable regulated direct current potential, means for connecting said input terminals of said pressure transducer across said source of selectively variable regulated direct current potential, means for connecting said movable contact of said poTentiometer and said movable contact of said pressure transducer across said second impedance element, and controllable switching circuit means corresponding to each phase of said alternating current supply potential for completing an energizing circuit for the corresponding said phase windings in response to respective said trigger signals.
 3. A speed control system for alternating current motors of the type having discrete phase windings corresponding to each phase of a compatible alternating current supply potential comprising, means for producing a reference potential in synchronism with a selected phase of said alternating current supply potential, means for producing a control potential which varies in magnitude with changes of motor speed, means including a unijunction transistor type relaxation oscillator circuit having a timing capacitor responsive to a difference in magnitude between said reference potential and said control potential for producing a trigger signal at the electrical angle of each potential cycle of each phase of said alternating current supply potential as determined by the magnitude of said difference, first and second impedance elements, means for connecting said reference potential across the series combination of said first impedance element and said timing capacitor, means for connecting said control potential across said first impedance element through said second impedance element in series in the same polarity relationship as said reference potential, a source of selectively variable regulated direct current potential, a potentiometer having a movable contact, a pressure transducer of the variable resistance type having two input terminals and a movable contact operated by changes of pressure, means for connecting said potentiometer across said source of selectively variable regulated direct current potential, means for connecting said input terminals of said pressure transducer across said source of selectively variable regulated direct current potential, means for connecting said movable contact of said pressure transducer to the same end of said second impedance element as said source of control potential, means for connecting said movable contact of said potentiometer to the other end of said second impedance element, and controllable switching circuit means corresponding to each phase of said alternating current supply potential for completing an energizing circuit for the corresponding said phase windings in response to respective said trigger signals.
 4. A speed control system for alternating current motors of the type having discrete phase windings corresponding to each phase of a compatible alternating current supply potential comprising, means for producing a reference potential in synchronism with a selected phase of said alternating current supply potential, means for producing a control potential which varies in magnitude with changes of motor speed, means including a unijunction transistor type relaxation oscillator circuit having a timing capacitor responsive to a difference in magnitude between said reference potential and said control potential for producing a trigger signal at the electrical angle of each potential cycle of each phase of said alternating current supply potential as determined by the magnitude of said difference, first and second impedance elements, means for connecting said reference potential across the series combination of said first impedance element and said timing capacitor, means for connecting said control potential across said first impedance element through said second impedance element in series in the same polarity relationship as said reference potential, an external source of current signals which vary in magnitude in response to changes of conditions which require a change of motor speed, means for applying said source of current signals across said second impedance element, and controllable switching circuit means corresponding to each phase of said alternating current supply potential for cOmpleting an energizing circuit for the corresponding said phase windings in response to respective said trigger signals. 